Imaging devices such as document scanners typically form images by collecting light reflected from an object, such as a document page being scanned, with numerous light-sensitive elements in a scan module. Each light-sensitive element is typically capable of producing an electronic output signal such as a voltage, which is indicative of the intensity of light reflected from a specific area or pixel of an image on the page. The scan module may be a stationary module for scanning a moving object, or it may be moveably mounted to scan a stationary object.
A backing member may be used to hold an object to be scanned against a transparent object support such as a glass platen. The backing member typically has a reflective white surface, although backing members of other colors may be used for the purpose of eliminating color “bleed through” when scanning certain documents, such as relatively transparent, dark, and/or double-sided documents. In cases where a document is fed into a device for scanning, it is desirable to sense presence of the document in a document load area. A document load sensor may be used for this purpose. The document load sensor may be mechanical or, more typically, optomechanical in nature. Upon sensing presence of a document, the document load sensor may trigger a feed mechanism to advance the document into the device for scanning.
In cases where the scan module is stationary, it may be further desirable to trigger a scanning procedure when the document reaches a scan region aligned with the scan module. This scanning procedure may be triggered by another sensor, which may be mechanical or optomechanical, and which may be similar in nature to the document load sensor. Use of two separate mechanical or optomechanical sensors, one to sense presence of a document in a document load area and another to sense presence of a document in a scan region, may add to the expense and complexity of manufacturing a scanning device.